Where those ideological differences most often show up, scholars say, is in the kinds of hot-button issues that attract significant public and media attention: abortion, capital punishment, affirmative action, environmental regulation, and discrimination based on race, sex, or disability.
Some legal analysts reject this view, saying it undermines the credibility of the judiciary. "I think it is a mistake to pay too much attention to the political party of the appointing president because that helps create a false impression in the public's mind that judges are and should be political actors," says James Swanson, a senior legal scholar at the Heritage Foundation in Washington.
David Klein, a University of Virginia political science professor, disagrees. He says federal judges have become important policymakers within the US government. "There are going to be major cases where they are making important policy that affects many of us where we can assume that ideology is going to play a role," Professor Klein says. "On the other hand, most of what they do probably isn't driven by ideology."
Although national attention is usually centered on the US Supreme Court when it attempts to resolve heated social issues, such disputes are fought out at the district and appeals court levels first. The regional appeals courts decide more than 63,000 cases each year, while the Supreme Court agrees to hear only 80 to 90 cases per term.
"As the Supreme Court's docket dwindles, the regional circuit courts become even more the Supreme Courts for their regions," says Carl Tobias of the University of Richmond School of Law.
Appeals court cases can be resolved in two ways. Three-judge panels decide the vast majority of federal appeals. But in certain cases, a panel decision can be further appealed to the full circuit court for so-called "en banc" review.
Republican appointees outnumber Democratic appointees in every federal appeals court except the Second Circuit in New York City (seven Democratic appointees to six Republican), the Sixth Circuit in Cincinnati (six Democratic appointees to six Republican), and the Ninth Circuit (16 Democratic to eight Republican).